A conventional input device will be described below. The conventional input device includes an actuator and a sensor electrode. The actuator has a first surface and a second surface, and includes a conductor. The first and second surfaces are formed on opposite sides of the actuator. The conductor is formed on the second surface. The actuator is disposed such that the conductor faces the sensor conductor. The actuator has a contact surface that is electrically connected to the conductor. For example, the contact surface of the actuator may be an area that is accessible to a person. Thus, the contact surface is formed at least on the first surface. The conventional input device gets a person's body to act as a ground when the person touches the contact surface with his/her finger. In other words, the touch causes a change in capacitance value between the sensor electrode and the conductor.
It should be noted that, for example, PTL 1 is known as a prior art document containing information related to the invention in this application.